设鸭为1,则鹅为2/5;则有：鹅比鸭少=(1-2/5)÷1=3/5;、鸭比鹅多=(1-2/5)÷(2/5)=3/2;鹅是鸭和鹅总数的几分之几？鸭是鸭和鹅总数的几分之几？鹅是鸭和鹅总数=(2/5)÷(1+2/5)=2/7; 鸭是鸭和鹅总数=1÷(1+2/5)=5/7